Function to find Average salary

Question

Hello everyone,
First of all I would like to say that I am a newbie to PL/SQL so please be patient with me. I am trying to create a function that will calculate the average salary for employees and compare the average salary to each employee's salary. If the employee's salary is lower than the average salary, my function will return true, elese it will return false.
I think I have a great start but need some guidance on what to do next. Here's my function so far:
CREATE OR REPLACE FUNCTION check_employee_salary
(p_empno IN NUMBER)
RETURN NUMBER
IS
lv_sal emp.sal%TYPE;
BEGIN
SELECT avg(sal)
INTO lv_sal
FROM emp
WHERE empno = p_empno;
RETURN (lv_sal);
END;
My function compiles but I can't figure out how to compare the avg(sal) to sal so that I can return true and false. Any guidance will be appreciated as I really want to understand PL/SQL and am trying very hard.
Thanks

Answer 1

Your function currently returns the average salary for a single employee, and since (in scott.emp at least) an employee only has one salary, it will return that.
SQL> select empno, ename, job, sal, check_employee_salary(empno) from emp;
     EMPNO ENAME      JOB              SAL CHECK_EMPLOYEE_SALARY(EMPNO)
      7369 SMITH      CLERK            800                          800
      7499 ALLEN      SALESMAN        1600                         1600
      7521 WARD       SALESMAN        1250                         1250
      7566 JONES      MANAGER         2975                         2975
      7654 MARTIN     SALESMAN        1250                         1250
      7698 BLAKE      MANAGER         2850                         2850
      7782 CLARK      MANAGER         2450                         2450
      7788 SCOTT      ANALYST         3000                         3000
      7839 KING       PRESIDENT       5000                         5000
      7844 TURNER     SALESMAN        1500                         1500
      7876 ADAMS      CLERK           1100                         1100
      7900 JAMES      CLERK            950                          950
      7902 FORD       ANALYST         3000                         3000
      7934 MILLER     CLERK           1300                         1300
14 rows selected.To report whether a specified employee's salary was above or below average, it would have to find the overall average (select avg(sal) from emp) and compare that to the specified employee's salary (select sal from emp where empno = p_empno). This would however be about the most inefficient way imaginable to derive this rather odd statistic. The easy way is using straight SQL:
select empno, ename, job, sal
     , avg(sal) over() as company_avg_sal
     , case when sal < avg(sal) over() then 'Below'
            when sal = avg(sal) over() then 'Average'
            when sal > avg(sal) over() then 'Above'
       end as comparison
from   emp;
     EMPNO ENAME      JOB              SAL COMPANY_AVG_SAL COMPARISON
      7369 SMITH      CLERK            800      2073.21429 Below
      7499 ALLEN      SALESMAN        1600      2073.21429 Below
      7521 WARD       SALESMAN        1250      2073.21429 Below
      7566 JONES      MANAGER         2975      2073.21429 Above
      7654 MARTIN     SALESMAN        1250      2073.21429 Below
      7698 BLAKE      MANAGER         2850      2073.21429 Above
      7782 CLARK      MANAGER         2450      2073.21429 Above
      7788 SCOTT      ANALYST         3000      2073.21429 Above
      7839 KING       PRESIDENT       5000      2073.21429 Above
      7844 TURNER     SALESMAN        1500      2073.21429 Below
      7876 ADAMS      CLERK           1100      2073.21429 Below
      7900 JAMES      CLERK            950      2073.21429 Below
      7902 FORD       ANALYST         3000      2073.21429 Above
      7934 MILLER     CLERK           1300      2073.21429 Below
14 rows selected.